JPS5824729B2 - Ultrasonic thickness measurement method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic thickness measurement device with improved stability and adjustment flexibility.

More particularly, an ultrasonic pulse reflection thickness measurement comprising a time interval averaging circuit cooperating with a programmable device to adjust the time interval average measurements required to measure the thickness of the piece being measured. Concerning a method and apparatus.

It is well known to measure the thickness of a piece to be measured using ultrasonic energy.

A typical measurement method that includes means for coupling an ultrasonic transmitting/receiving probe to the surface of a piece to be measured periodically; emitting ultrasonic probe pulses into the piece to be measured; Receives reflected waves from collisions with the front and rear walls.

The time measurement gate circuit starts operating in response to receiving a reflected pulse from the entrance surface, and stops operating in response to receiving a reflected pulse from the rear wall.

The time interval between the reception of the two pulses, ie the width of the generated time measurement signal, reflects the thickness of the piece to be measured.

Difficulties have been encountered with devices of the prior art in determining the value of the thickness of a piece to be measured from the time measurement signal pulse width.

In particular, when analog circuitry is used to determine the thickness, a constant current generator and a ramp signal generator are required.

For example, U.S. Pat. No. 3,485,0 by Brech
Please refer to No. 87.

Such devices have a problem in stably maintaining the linearity of the lamp signal waveform as the operating temperature changes and the electronic circuit components age.

A common method of generating a ramp signal waveform is by charging a capacitor with a constant current for an interval corresponding to the width of the time measurement signal.

The capacitor integrates the constant current with respect to time, thereby generating a lamp voltage signal waveform.

The highest value of the lamp voltage signal represents the width of the time measurement signal.

The stability of current sources and capacitors varies over the normal operating temperature range, which negatively impacts the stability and accuracy of thickness measurements.

Other prior art techniques have used digital circuits with improved drift, drift, and stability characteristics compared to analog circuits, which required the use of stable, high frequency clocks.

High frequency clocks tend to generate noise in the circuit,
Consumes excessive power.

Piece of aluminum to be measured. When measuring the thickness, set the thickness to 0
．． To measure with a resolution of 0.3 mm, a clock frequency of 125 MHz is required.

Furthermore, in order to measure the thickness of specimens with different sound velocities, the clock frequency must be changed accordingly, requiring an expensive tuning device with stable characteristics over a temperature range. It becomes necessary.

Alternatively, to measure the thickness of materials with different sound speeds, multiple high-frequency clocks, each oscillating at a different frequency, are required.

Other prior systems use vernier counting methods that employ bistable, accurate, and expensive locking circuits.

The Vernier counting method was developed in 1965 by McG
It is explained in ``Pulse, Digital, and Switching Waveforms'' by Millman and Taub, pp. 683 to 687, published by Raw-Hi Ill.

Time interval averaging was also used in some previous devices to improve the stability and resolution of thickness measurements.

As described above, a time measurement signal is generated with a pulse width that depends on the thickness of the piece to be measured.

The pulse width is determined by counting the number of pulses (T) from the high-frequency clock pulse that occur during the interval of the time measurement signal, and dividing this number of pulses by a constant N to obtain the number (T) for each measurement.
P/N).

Note that the constant N is the fixed value N of the N frequency divider that divides the number of pulses.
It is about.

The number of measurements performed (N/) is the first average of the number of clock pulses counted during the time measurement gate interval.
It is made equal to N in order to find it by Eq.

Time interval averaging methods improve resolution compared to digital measurement methods and also increase stability by averaging out the ever-present white noise.

Although time interval averaging systems offer these advantages, they are not suitable for calibration because the number of measurements N', the numerator of the first equation, is fixed.

In order to maintain time-resolution when measuring specimens with different sound speeds, separate clocks or adjustable locks are required for each different sound speed, requiring expensive and complex equipment.

In the device of the invention a modified version of the time interval averaging circuit of the type described above is used.

A programmable counter, such as a programmable divide-by-N counter, is provided for the purpose of calibrating the device to measure the thickness of specimens having different sound velocities.

In a preferred embodiment, the programmable counter is programmed by a suitable device, such as a thumbwheel switch, to a value representative of the speed of sound in the specimen being measured.

Number of measurements (Q equals the value programmed into the programmable counter.

The number of pulses that occur during the time interval of the time measurement gate is the second
It becomes like the expression.

The pulse width of the time measurement signal is equal to the time 2Xi8 required for the ultrasonic signal to travel twice across the thickness of the specimen at a velocity V.

The number of clock pulses for a given time is equal to the clock frequency f.

The constant value N for obtaining the average number of pulses of each measuring vehicle is left unchanged, and the second equation becomes the third equation.

When the number of measurements (Q) determined by the programmable counter is equal to the sound velocity (7) of the piece to be measured, the third equation becomes the fourth equation.

If frequency f and frequency division number N are 5×10(n-1)
If the index (n-1) depends on the frequency f and the size of the frequency division number N, then the fourth equation becomes the fifth equation.

A suitable division by 10 will reveal that the number of pulses counted is equal to the thickness of the piece being measured (nt).

When the ratio differs from 5.times.10.sup.2, an additional scaling circuit according to known techniques is used to convert the number of counted pulses into a representation of the measured thickness.

This thickness measuring device can be easily calibrated to measure the thickness of any piece being measured.

If the sound velocity of the piece being measured is unknown, a sample piece having a known thickness is measured.

The programmable counter is adjusted until the displayed thickness equals the known thickness.

The described device has advantages over previous devices, but no disadvantages.

Because the device uses digital circuitry, the disadvantages inherent in analog constant current generators and ramp signal generators are eliminated.

A programmable device that changes the number of measurements before displaying a thickness value allows the use of a single clock with a fixed frequency, which is lower than that used in earlier digital measurement devices. be.

The thickness measuring device according to the invention can be used to measure the thickness of pieces with different sound velocities without the need to change the clock frequency.

Furthermore, the traditional difficult problems of stability and drift have been eliminated.

Accordingly, a primary object of the present invention is to provide an ultrasonic thickness measuring device that includes a programmable device for use with a time interval averaging circuit.

Another principal object of the present invention is to provide an ultrasonic thickness measuring device that includes means for calibrating the device to measure specimens with different sound velocities.

Furthermore, it is an object of the present invention to provide a device with a programmable device that can be easily calibrated for any sound velocity required by the piece being measured and is characterized by increased stability and resolution. An object of the present invention is to provide an ultrasonic thickness measuring device.

Referring to the figures, there is shown a schematic block diagram of an embodiment of the present invention.

The repetition rate clock 10 is periodic, typically 500 Hz.
Timing pulses are provided to the pulser 12 to excite the transceiver probe 14 at a frequency between 20 KHz and 20 KHz.

The transmitting/receiving probe 14 responds to the electrical signal from the pulser 12 by periodically transmitting ultrasonic probe pulses into the piece W to be measured whose thickness is to be measured, and receives reflected response pulses.

These reflected response pulses are converted into electrical signals by the probe and supplied to the receiving circuit 16.

The receiver circuit 16 then supplies a reflection response trigger signal to a timing flip-flop 18 to generate a thickness response time measurement signal corresponding to the propagation time of each probing pulse through the test piece.

Here, one time measurement signal is generated for each probing pulse supplied by the probe 14.

Clock 20 supplies a pulse train of a predetermined frequency to gate circuit 22.

The time measurement signal from flip-flop 18 opens gate circuit 22 for a time interval equal to the width of the time measurement signal corresponding to the thickness of the piece W to be measured.

A counting device 24, such as a divide-by-N counting circuit in the preferred embodiment, is connected to the output of the gate circuit 22 and receives pulses from the clock 20 through the gate 22, which is open during each time measurement signal interval. , and provides an output count signal that displays the number divided by N.

A counter 26 is connected to the counter 24 for integrating and storing the output count signal of the fixed N-frequency counter 24.

The accumulated number of pulses in the counter 26 is calculated by the readout device 2.
In response to the update signal being sent from the update circuit 30 to 8,
A readout device 28 is provided.

In the preferred embodiment, the counter 24 is a fixed divide-by-N counting circuit that outputs a count when N clock pulses are received and taken by the counter 24 from the clock 20 through the open gate circuit 22. Any combination of counting circuits and logic circuits can be used so that .

A programmable counting device 32, which in the preferred embodiment is a programmable N fraction counter, is connected to the object whose thickness is to be measured by an addressing device 34, such as a thumbwheel switch or other suitable regulator. The speed of sound is preset to one side.

For example, try 6.35 X 1 o5crrL,'
In the case of a piece of aluminum to be measured with a sound velocity of SeC (2,5X 105inch/5ec), when measuring its thickness in metric system, change the thumbwheel switch display to r6.
When setting to 350J or measuring in American units, change the thumbwheel switch display to l'-2300.
Set to J.

Counter 32 counts the number of timing gates sent from clock 10 to pulser 12.

Then, this will count the number of intervals of the time measurement signal.

When the number of timing pulses from the clock 10 being counted by the programmable counter 32 is equal to the preset number of the address device 34, one signal is sent from the counter 32 to the update circuit 30 and the delay circuit 38. will be sent.

The reading device receives the count value from the counter 26 and updates its display contents.

After a delay sufficient to ensure that the readout device 28 receives the update signal, the reset signal is transferred from the delay circuit 38 to the counting device 2.
4 and counter 26 to reset both circuits to zero.

□The counter 32 is also reset by itself to repeatedly count the preset number of timing pulses.

The transceiver probe 14 is coupled to the surface of the sample by suitable coupling means, such as oil or water, to transmit ultrasonic energy to measure the thickness of the sample.

The sound velocity of the piece being measured is programmed into the programmable divide-by-N calculator 32 by an addressing device 34, such as a thumbwheel switch.

The periodically occurring timing pulses transmitted from the repetition rate clock 10 to the pulser 12 cause the pulser to probe 1.
4 is periodically excited.

probe 14 in response to each supplied pulse signal.
sends an ultrasonic energy probing pulse into the specimen and receives response reflection pulses from the incident surface and rear wall of the specimen.

The received reflected pulses are converted into electrical signals by probe 14 and sent to receiver 16 .

Receiver 16 provides an output trigger signal to timing flip-flop circuit 18 .

Timing pulses are also communicated from clock 10 to timing flip-flop 18 to reset timing flip-flop 18 at the beginning of each respective period.

The video output quadratic pulses obtained from the receiver 16 that are responsive to the reflected pulses at the input surface start the timing flip-flop circuit 18 and those that are responsive to the reflected pulses at the back wall are stopped.

The pulse width of the resulting time measurement signal output corresponds to the distance traveled by the ultrasonic pulse signal through the specimen during the interval of the trigger signal, or the thickness of the specimen.

A time measurement signal obtained from the timing flip-flop circuit 18 having a pulse width equal to the thickness of the piece being measured is sent to one input of the gate 22 to open the gate 22 during the presence of the time measurement signal.

Clock 20 provides another clock pulse to the other input of gate 22.

In the preferred embodiment, the frequency of this clock pulse is 12.8 MHz, which is significantly higher than the frequency of repetition rate clock 10, which is typically 10 KHz.

When gate 22 is open during the time measurement signal interval, clock pulses from clock 20 are transmitted through open gate 22 to fixed N divider counter 24.

Counter 24 generates an output count signal every time it receives N pulses from clock 20.

The value of N in the example shown is chosen such that the ratio of the megahertz frequency of clock 20 divided by N is equal to 0.05.

In this example where the clock frequency is 12.8MHz, N is 2.
Selected as 56th.

It will be apparent that the time measurement signal from the timing flip-flop is asynchronous with the clock pulses from clock 20.

In other words, the opening and closing of the timing gates are not simultaneous with the clock pulses from clock 20.

The number counted by counting device 24 will therefore vary due to the time at which each time measurement signal occurs relative to the clock pulse from clock 20.

Counter 24 generates a count signal, one for each N pulses during each time measurement signal interval, and sends a count output to counter 26 for accumulating the number of counts obtained from counter 24.

After a predetermined number of measurements have been made, i.e., after obtaining time measurement signals from a predetermined number of flip-flop circuits 18 programmed into the counting device 32 by the addressing charge 34, the counting device 32
A signal is supplied from the update circuit 30 to the update circuit 30.

In response to the signal from the counting device 32, the update circuit 30 sends an update signal to the readout device 28 to display the thickness of the specimen equal to the number of counts accumulated and stored in the counter 26.

The reading device 28 stores the display until the next subsequent update signal.

The output signal from the counter 32 is delayed by a delay device 38 for a sufficient time for the readout device 28 to be updated with the value in the counter 26, and then resets the fixed divide-by-N counter 24 and the counter 26. is supplied from delay device 38 to do so.

One of the features of the invention is a method for calibrating a thickness measuring device.

In the foregoing description, the sound velocity of the specimen being measured was known and programmed directly into the programmable N divider by the addressing device 34.

In other applications, the velocity of the ultrasound signal through the specimen is unknown.

In such a case, a sample of the piece to be measured of known thickness is ultrasonically coupled to the probe 14.

Addressing device 34 in combination with programmable counting device 32 is then adjusted such that readout device 38 displays a value consistent with the known thickness.

The readout device may be in American units (inches) or metric (cenmeters), but once adjusted, readjust it when measuring a piece of unknown thickness with the same speed of sound. There's no need.

In the known ultrasonic thickness measuring device that uses time averaging, the number of measurements (update period) is kept constant.

In that device, the repetition rate or frequency of the clock was varied, thus requiring an expensive tuned clock circuit to change the frequency.

In this embodiment, the number of measurements performed is programmable for the sake of instrument calibration practice.

The use of digital circuitry in conjunction with the device's scale adjustment device has advanced the ultrasonic thickness measurement device in terms of stability, accuracy, and resolution compared to previously known devices.

In the foregoing discussion, the beginning of the timing gate from timing flip-flop 18 is triggered by a signal responsive to the input surface response reflection pulse.

It is clear that the start trigger signal can also be generated by an adjustable monostable multi-bi break connected between the repetition rate clock 10 and the timing flip-flop circuit 18.

The pulse width of the multi-by-break is adjusted to provide a trigger signal such that the timing flip-flop 18 is delayed during the time interval between generation of the timing signal by the clock 10 and the entry of the ultrasonic probing pulse of the probe into the specimen. Ru.

The use of such an artificial start trigger signal eliminates the need for a suppressor to dampen the ringing of the probe 14 during the expected time of the incident surface response reflection pulse.

The problem is that the probe is in direct contact with the surface of the piece being measured, and the time from the timing pulse to the beginning of the time measurement signal from the timing flip-flop 18 is passed through a relatively thin wear plate placed in front of the probe 14. It is especially intense when it is equal to the time taken by the ultrasound signal.

As an alternative embodiment, one or both of the counting device and the time measuring device are suppressed by a suppression gate connected to the receiving device 16 for a fixed period of time after the time the probing pulse is sent to the test piece.

It is connected in a known manner to cause the timing flip-flop circuit 18 to respond only to a pair of reflected signals caused by reflections from the back wall which are received after the input surface response reflected signal.

It is of course possible with known techniques to measure the time interval between two discrete back wall reflection pulses.

It is clear that in both embodiments it is necessary that the count in counter 26 be divided by a suitable divisor.

It is most advantageous to provide an addressing device that is programmed to indicate the speed of sound of the piece being measured by means of a scale, while at the same time adjusting the frequency of the clock 20 and the counting device 24.
The address device 34 may be modified by selecting the ratio of the value N of the address device 34 to a value other than 5×10 (n″″1) or by using an additional lock or counting device in the circuit.
It is also clear that can be programmed for any arbitrary unit.

As previously discussed, the signal from counter 26 is provided to digital display readout 28.

However, it is clear that the signal from the counter 26 can be fed to other display or indicating devices or to signal processing devices.

For example, when classifying a specimen, the output signal is connected to a digital comparator to generate an accept/reject signal when the thickness of the specimen is within a predetermined tolerance level. obtain.

The output signal may also be provided to a digital-to-analog converter, the output of which is connected to a chart recorder.

In other applications, the output signal may be fed to a computer for further signal processing and analysis without being displayed.

While the present invention has been described and illustrated with respect to the presently disclosed embodiments and certain variations thereof, the present invention is to be limited only by the scope of the appended claims. It will be obvious to those skilled in the art that this can be done without departing from the essence of the invention.

[Brief explanation of the drawing]

The drawing is a schematic electrical block diagram showing an embodiment of the ultrasonic thickness measuring device according to the present invention.

Claims (1)

[Claims] 1. A method for measuring the dimensions of an object to be measured by an ultrasonic pulse reflection method, comprising: (a) periodically transmitting ultrasonic probe pulses to the surface of the object; receiving reflected pulses responsive to the probing pulses being interrupted by acoustic impedance changes; c) providing a count corresponding to the propagation time of each probing pulse across the dimension of the measured object from the surface to the point of impedance change, as determined by the time interval between the reception of the signal of C.2; 2) accumulating the counts supplied during such consecutive time intervals; and 2) accumulating the counts when a predetermined programmable number of probing pulses representative of the sound speed of the object being measured have been sent. providing an output signal responsive to the counted count. 2. The method of claim 1, wherein the predetermined number of probing pulses is programmable by an adjustable device. 3. The method of claim 1, wherein the count is a discrete relock pulse. 4. The method according to claim 1, wherein the first signal is in response to a probe pulse incident on the surface of the object to be measured, and the second signal is in response to the probe pulse incident on the surface of the object to be measured. 5. The method according to claim 1, wherein the first signal is in response to the probe pulse being blocked by a rear wall of the object. said second signal being in response to a subsequent reflection of ultrasound energy provided by said probing pulse at a back wall. 6. The method according to claim 4, wherein the first signal is an electrical signal generated after a predetermined time after sending out the probe pulse, and the second signal is an electric signal generated after a predetermined time after sending out the probe pulse. said method in response to a reflected signal originating from a rear wall of said device. 1. The method of claim 1, wherein the output signal provides a succession of measured dimensions. 8. The method of claim 1, wherein the predetermined number is programmable in units of sound speed. 9 An ultrasonic device that measures the dimensions of an object to be measured by periodically transmitting a probe pulse into the object and subsequently receiving a reflected pulse in response to the transmitted probe pulse, ) a first clock for supplying a timing pulse; and a) a pulse generator connected to receive the timing pulse and supply a signal for transmitting a periodic probing pulse into the object under test in response. and c) a receiver connected to receive the reflected response pulse in response to the transmission of each probe pulse; and 2) a receiver connected to receive the reflected response pulse in response to the transmission of the respective probe pulses; a distance traversed by the probe pulse within the object to be measured for receiving a second signal in response to a reflected response pulse associated with the probe pulse and during a time interval between the fourth signal and the second signal; e) a second clock for providing periodic rank pulses; and f) a second clock for receiving said periodic rank pulses; a counting device connected to receive the time measurement signal and thereby provide a third signal in the form of a count corresponding to the number of periodic clock pulses occurring during the time measurement signal; ) a counter connected to receive said third signal and a plurality of subsequent third signals for accumulating a count corresponding to each number of periodic clock pulses occurring between successive time measurement signals; and h) in response to said timing pulse, a receiver is adapted to said first clock for providing a fourth signal when the number of timing pulses taken is equal to a programmed number representing the sound speed of the object being measured. and a) a programmable counting device connected to the counter and the programmable counting device for providing a reading corresponding to the accumulated count in response to the fourth signal. and a reading device. 10. The device according to claim 9, wherein the time measuring device comprises a flip-flop circuit that starts in response to the fourth signal and stops in response to the second signal; connected to the first clock and the flip-flop circuit for receiving a timing pulse and providing a trigger signal to the flip-flop circuit for starting the flip-flop circuit a predetermined time after receipt of the timing pulse; said device, including another device that contains said device. 11. The apparatus of claim 9, including means for connecting said time measuring device with said first clock for periodically resetting said time measuring device in response to said timing pulse. Device. 12. The apparatus of claim 9, wherein the counting device includes a gate connected to receive the clock pulse with a first manual input and to receive the time measurement signal with a second manual input, a clock pulse passes through the date during the time interval between the first and second signals, and the counting device calculates the third signal in response to the number of the clock pulses passing through the gate. said device comprising a divide-by-N counter connected to said gate for supplying said gate; 13. The apparatus of claim 9, wherein the programmable counting device comprises an addressing device and a programmable divide-by-N counter, the addressing device comprises a settable switch, and the programmable counting device comprises an address device and a programmable divide-by-N counter; Said device in which a switch is associated with a scale for indicating the sound speed of the object being measured. 14. The device of claim 9, wherein the readout device is a digital display device. 15. The device according to claim 9, wherein the counting device and the counter are arranged periodically? The device wherein the fourth signal is connected to the counting device and the counter for setting the stiffness. 16. The apparatus according to claim 9, comprising a conversion probe connected to the pulse generator and the receiver, and adapted to be coupled to an object to be measured. 17. The apparatus of claim 16, wherein the first signal is an entrance surface reflection response signal and the second signal is a back wall reflection response signal. 18. The apparatus according to claim 16, wherein the first signal is a rear wall reflection response signal, and the second signal is intercepted by the rear wall of the object to be measured after the probe signal. said device responsive to ultrasonic energy supplied thereto.